Modulators and demodulators are used within transmitting and receiving devices in mobile stations in order to modulate a carrier wave and received data in accordance with the data to be transmitted, and to demodulate the received data in a corresponding manner, in accordance with standardized modulation and demodulation methods. Known modulation and demodulation methods are, for example, GSM (Global System for Mobile Communication), EDGE (Enhanced Data Rates for GSM Evolution), TIA-EIA 136 (Telecommunication Industry Associations/Electronic Industry Association), UTRA FDD ((UMTS-Terrestrial Radio Access Frequency Division Duplex), UTRA TDD (UMTS-Terrestrial Radio Access Time Division Duplex) and IS-95. In general, these modulators and demodulators comprise a baseband component and a radio-frequency component. During transmission, the baseband component makes use of digital signal processing to convert the data which is to be transmitted to a generally complex-value signal which complies with the standard. The signal is converted by the radio-frequency component to a radio frequency, and is transmitted after suitable amplification via an antenna as a real-value signal. In a corresponding manner, during reception, the received payload data is demodulated by the radio-frequency component to form a complex-value signal, and the received demodulated data is processed further in the baseband component.
Since the physical requirements for the baseband and radio-frequency components differ, these functional units are generally produced in separate integrated circuits (radio-frequency chip and baseband chip) using different manufacturing technologies. In the transmitting direction, the modulated baseband signal must be passed in suitable form to the radio-frequency component. In the receiving direction, the demodulated radio-frequency signal must be converted in a suitable form to the baseband signal. A suitable interface must be provided between the baseband component and the radio-frequency component for this purpose.
Currently, the payload data is normally transmitted in analogue form between the radio-frequency component and the baseband component. The payload data signals are in this case normally produced by the analogue interface as complex-value baseband signals, which are subdivided into a real part and an imaginary part (so-called in-phase (I) component and quadrature (Q) component). Both the I component and the Q component are generally transmitted as a differential signal, that is to say at least four lines are required for bidirectional payload data transmission.
This form of signal transmission has the disadvantage that relatively high-quality analogue signal processing components, such as digital/analogue and analogue/digital converters, must be provided both in the baseband component and in the radio-frequency component.
The requirement for the baseband component to be equipped with analogue and digital circuit components as a mixed signal module (hybrid module) in particular increases the price of its development and manufacture. The circuit components that are required for production and transmission of the differential analogue signals in particular occupy a significant proportion of the chip area, even though they are not required for the actual baseband signal processing.
Furthermore, special signal processing steps often have to be carried out in the baseband component in order to compensate for or to correct for inadequacies, non-ideal features or tolerances in the radio-frequency component, in advance. In consequence, the baseband component can no longer be regarded, analyzed and developed independently of the radio-frequency component. As a result of the progress in development in the field of digital signal processing and modulator and demodulator concepts, the proportion of processing in baseband in the overall signal processing path is increasing, particularly with regard to the interaction with the radio-frequency part. This results in an undesirable restriction to the flexibility of baseband components or baseband chips, since the baseband component can only be used together with those radio-frequency assemblies for which they have been especially developed.
German Laid-Open Specification DE 100 35 116 A1 describes a conventional analogue radio-frequency interface for dual-standard baseband chips in mobile radios.